Slip clutch for screw actuators



Nov. 24, 1953 L. ocHTMAN SLIP CLUTCH FOR SCREW ACTUATORS Filed Feb. 25, 1949 Patented Nov. 24, 1953 SCREW ACTUATORS IqegnardrOchtman, Ridgewood,` N; Ja', assignorito'- YRendi-irA-vitttioli Corporation, Teterboro;v N' JE,

arcorporationeofiDelaware Appiiationql'ehruary Z5, 19.49,.,Serial -N..78,"3631`.

51'Glaims:` (Cl. 19.2'-141) 'l1he.nresentinyenti9n. rentes .eenerellxtw- @niort and, nere psrtieulerlr. to etrex/e121 limiting clutch forlanmagtuator of ,the srew Jael; type. 'best exam.. asenfeziamnle f,;`the,.pre sentginyenr tion .is Cpnstiiuted substantielle, as eloneitudif eiensble ,111115. qempriene. en axallx rela: f? Y ble 'husins and." anelensatedarm agent di@ operate@ el?- @nt piganairplane-sueh as alten .O f. flea bythe/ins.. oifceurse-menr other applications.,`

eeimeiien.Wthnh applations, the Afictileter is Ordinarily. D, vided' with mechanica stops at onehor Ylocgthextjm eine positionsorder to prevent* over-tr,avelf of the members operated the by;` This,A of bourse, results in asuddenarf rest; o fjnotionfoffthe operati-ngfV-parts o fjthe'ace tatorvandjmay ,cause unduey stresses and excessiveY wear-thereof? In order-to-reduce 'the shock-- loa@ ithas-been common practice -to tcie-energize the driviiigfrneclfianisn?justpriorto thecontact oftherespetive-stepsbuteven soethe resulting shookr--loadjhas beer-1! al causeof-feoncerny to-de sinersz if,J forsomereason'; the drivingmechanism-.isnot' cutw--prior-to the vcontaetf-orfethe Steins.,r failure 4of-paits -is likely-to occur unless `the partslvofi the actuator-are designed ymuch heavier thanneeessaryfor normal operation:-

' One-.object-o the presentf-inventionfisto--provide a simple, effective and novel clutch for@` an actuator.. `wh'ieh.-.v.1il-l.Y prevent overloading.. offfthe operating-mechanism thereofuif: the `driving :pow-er is.;notscut.,oinspriornte the 1contact.. of ;the:stop members AnQthenobjeCt eislto ,prov-.ide .arsimpla effective andsnovel 'clutehfwhich willproteet .thefoperating mechanism.against .excessive wear dueto sudden stops.andlreversalstthereot.

Anotherobject is. toprovideua clutch for anfactuator of the screwjaclytypewhich utilizes. the thrust `of i th'e-j aelmserew fion -loading -the-friction surfaces whereby suchfrictionfsurfacesjandloading-springs-Inay-be'made verysmallal` eenA for- -preloading the friction suriaeespf 'anjactuatori-'clutchiinlof'derQto ensure positive gripping action therebetween inl-.hev algjs e ii ce`y of thrust on theiekserew.

Still'. another Orient-isz. iq provide .an actuator wherein the stops of jthe'k extensible; member e are arranged "S'i as `,riot l-to `cause vad ditic nal `thrust v on the Screwrrlleber 1112911 .enges ent ,the Qtr.

and'durable in construction, economical tomarmefacture and effective in its operation.

These and other Aobiects.andf'featuresofitiieirrivention are pointediout'inthe followingfd'escription, in terms ofJ the" illustrated' embodiments thereof which" are shownin trie accompanying drawing. Itis-understcodjhoweverfthattlreillus# trations are gfor; the' purposeof exampleoniyrand are not' intendedias ai definition" of"`th"e limits A`of the, invention, referencee heingv had' to the"7 apipended- 4claims, for-'this purpose? In the drawings:

Figure 11 is 'aiside nvievsrpartially'ir'e1evationemtl partially'in" section of 4an actuator'embodyingj'tlie trave1 limiting` clutch and Jotherfeat-ures offene present invention. Y

Figure 2 shows a'modii'cati'onoftliecltifsurf faces shown in Figure n1 The device Vshown"innFigure'l-1comprisesfinegerre eral' a housing 10 "havingghousingj portions el 2` and -fenclosing an actuator 'ofrthe'serew :jacktype arm I8, clutch-20; gear-train- 22;Q andfthe driving means-generally indicatediatZ- The deviceas a vwhole-isl'adaptecl' toV vbefpivotally mounted on( a. suitable- *fha-sefas `byffa bolt extend!- ng through a -h'ol -2 6)@ inftheJhousingeportion' I 2i The 'screWshaftf i Sf comprisesa'f-shankiportin' 2 8 and--screw portion-3&1 and is'jo'urnalect to theiiousf ing I il'4 'by bearing S2-*and -fthrough-'the*cliithrZlt by ball bearings 361 Annular Ting memberse38`-`and 3 9' are keyedfitthe shank portionwZlby-keys bandld-frespee tively in such a manner-thatthe -fri'ngs will rotate withthe shaft=butare=f1eetoslide-iongitudinailv thereon. Ring fmembers v3 8 and '=39""l`1avecone= shaped surfaces# 2' 'and l'4i-3 l1'espec-:tively Vfacing-feaeh other andfadaptedtoumate withNcor-responding cone-shaped surfaces i4-andiE'fofdriving ring-'46 and driving gear t8respeeti-veli?.-v Th'e drivingring has a-hub portion 56 lprovided withjaw-'teeth adapted to engage A cor-responding" jaw'teethf. 51 of.` ithe hub' por-tion *521`0fthe lohiv'ing` gearridibut they emayv .of 'courseberjontedi b'y: any convenient means;l lntheroonstruetion showni'nidshe edraw ing, the inner :araceiofxbearingi mise securelgggheld betweenjthe hub .pprtionsofvthe drivinggearY 46 Yand,.driving gear` .f liandr. ng-aitrecessefermed therein. The outer race. of bearing 36; ismmounted ,bes tweenthe housingportions. l 2..,ar'1d4 I 4 -as showrrn the drawings sol astoJoe able: toresistaxial. thrust in either direction.- Y i i I The .threaded endg-portion ofv the Ashaftf'll Slisof a smaller diameter than the shaft thus providing` a shoulder 55 against which washer 51 and the lock washer 58 are held by a nut 88. Between washer 51 and a back face 82 of ring 38 is clamped one or more belleville springs 64 in order to exert a pressure against ring 38 which pressure is in turn transmitted to the mating cone surfaces 42, 44 and 43, 45, the purpose of which will be apparent as the description proceeds. The tension and gap of spring 54 may be adjusted by inserting one or more shims 65.

Driving gear 48 is shown as being driven from the driving means 24, which may be an electric motor, through a pinion 86.

The extendable arm I8 is shown in the drawing provided with terminal means 10 for connection with the member of the airplane to be operated, either directly or through a linking mechanism. The terminal 18 may be brazed or otherwise secured to one end of a tube 14 which surrounds the screw portion 30 of the shaft I6 and has its other end secured to an internally threaded nut 18 adapted to cooperate the threads of the screw portion 38. The nut 18 is shown as being provided with stop lugs 88 and 82.

The back face of ring member 39 abuts a sleeve 84 which is keyed to shank portion 28 of shaft I6 and is kept in position as by a collar 85 made integrally with the shaft. Sleeve 84 which may be made integrally with the shaft i6 is adapted 4to rotate within bearing 32, and is provided with a stop lug 88 adapted to engage stop lug 80 of nut 18. A similar stop lug 98 is secured to a ring member 92 which is splined or otherwise secured to the extreme end of screw portion 38 of the shaft I6 in order to fix the outward limit of travel of the nut 18.

Figure 2 illustrates a modification of the clutch 20 of Figure l, like reference numerals indicating corresponding parts, in which the clutch friction surfaces are shown as disc-shaped surfaces 94, 95 and 96, 91. Gear 48a is supported on the shank portion 28 of the shaft I6 by a bushing 98 which may be press tted in the hub 52a.

The operation of the device is as follows:

The screw shaft I8 is driven from driving means 24 through a gear train 22, comprising the driving gear 48 and output pinion 66 and clutch 28 whereby the arm I8 is forced to the right by the interaction between the threads of the screw shaft and the threads of the nut 18 which nut is constrained from rotation by the member of the aircraft to be operated or by a spline in the extended housing portion 83. The backward thrust resulting from the force applied by the terminal means 18 against the member to be operated upon is transmitted through the collar 85, sleeve 84 and driving ring 39 to the coneshaped surfaces 43 and 45 of the clutch 28. It Should be noted that the friction between these surfaces is proportional to the backward thrust against shaft I6 and will prevent the clutch from slipping as the load increases. The diameter and angle of the cone surfaces may be so proportioned that with normal friction coefficients the eective torque capacity of the friction surfaces will always be substantially higher than the driving 'torque required. It should be noted that the driving torque is directly proportional to the thrust on the driving screw and that the torque capacity is a direct function of the thrust imposed on the screw by the working load. The cone may be made to have any degree of angle required for a particular design of the actuator, and it may even divert from a cone-shape altogether if at driv- 4 ing surfaces such as shown in Figure 2 would better meet individual requirements.

The nut 18 will continue to drive the arm I8 to the right, unless the driving means 24 is deenergized or disengaged, until the stop lug 82 of the nut 18 engages the stop lug 98 of the ring member 92 thereby preventing the shaft from further rotation. The illustrated cooperating 'stop lugs 80, 88, and 82, 98 may, of course, be substituted by other convenient means for arresting the relative axial movement between the shaft IB and the extendable arm I8 which do not thereby increase the external thrust on the shaft and friction surfaces. Suitable means are provided for de-energizing the driving means 24 or disengaging it from the gear train 22 just prior to the engagement of the stop jaws but as such means are well known in the art and form no part of the present invention detailed description thereof has been omitted in order to render a more clear description of the invention.

When further turning of the shaft I6 is prevented by the contact of the stop lugs 82 and 90, the backward thrust on the shaft is not thereby increased and the force applied against the cone surfaces 43 and 45 will not be affected. If the driving power is not shut off or if the kinetic energy left in the gear train 22 and driving means 24 is sufiicient to continue to apply force to the clutch the cone surfaces will slip with respect to each other thus preventing excessive loading on the shaft and associated parts.

When it is desired to return the arm I8 to its retracted position, the driving means 24 is reversed thus forcing the nut 'I8 and arm I8 to travel towards the left as viewed in the -drawing. This results in an outward axial thrust on the shaft which thrust is transmitted to friction surfaces 42 and 44 through washer 65 and compressed spring 64. As was previously pointed out, the driving ring member 38 is mounted on the shaft I 6 in such a manner that the ring will turn with the shaft but is free to slide longitudinally thereon. The driving torque between the friction surfaces 42 and 44 and thus between the clutch 28 and shaft I8 is proportional to the axial outward thrust on the shaft I 8 and the same considerations apply in this case as those discussed in yconnection with the driving surfaces 43 and 45.

In the particular embodiments of the invention illustrated in the drawing, the friction surfaces are shown to be symmetrical, while in certain applications it may be found advantageous to make one cone surface steeper or larger than the other depending on the requirements of the particular case. It may even be found preferable to combine the features shown in Figures 1 and 2 thus making one friction surface coneshaped and the other disc-shaped.

One or more springs I84 are placed between the washer 51 and the back surface 62 of the slidable ring 38 in order to preload the friction surfaces so as to prevent them from slipping when no axial thrust on the shaft is present in either direction. The amount of preloading needed will depend on the requirements of the particular actuator in question. Clutch shims 65 are provided for adjusting the gap of the spring 64- It has been found that satisfactory operation is obtained if the spring is compressed within 0,003 of an inch of its fully compressed state.

Although only two embodiments of the invention have been shown and described, it is to :be

understood that these are to be'taken only as preferred examples of the invention and that various changes in the shape, size and arr-angement of parts may be resorted to without departing from the true scope of the invention or the appended claims.

What is claimed is:

1. In an actuator, the combination of a housing having an actuator pivot mounting end, a reversibly rotatable shaft including a longitudinal inner end section journaled in said housing adjacent to said pivot end, said section carrying an outer end clutch jaw and the shaft having an outer end screw portion protruding from said jaw, an elongated element along said screw having an outer end constituting the other actuator pivot mounting end and embodying an inner end nut on said screw, said section having a clutch jaw complemental to said rst clutch jaw, said section including a length of reduced diameter providing a shoulder axially inwardly of said jaws and a screw shank of further reduced diameter providing a stop axially inwardly ofsaid shoulder, a pair of rings axially spaced from each other around and secured to said length for rotation therewith and axial movement relative thereto and having peripheral friction surfaces axially facing each other, one of said rings being backed by said shoulder, a bearing held to said housing axially intermediate said surfaces and adapted to resist thrust in each axial direction, driving gear and annulus members around said length axially embracing said bearing between said rings and having friction surfaces complemental to said ring friction surfaces, respectively, said gear and annulus being connected for rotation with and axial movement relative to each other, shim means next to the other of said rings and spring means next to said shim means around said length, and a washer against said stop next to said spring means, a washer lock next to said washer, and a nut next and locked to said lock around said screw shank.

2. The combination of a reversibly rotatable shaft, means associated with said shaft to selec,- tively subject said shaft to opposite axial thrust loads, elements axially spaced from each other around and connected to said shaft for rotation therewith and axial movement relative thereto and having axially oppositely facing friction surfaces, means adapted to resist thrust in opposite directions, driving members around said shaft engageable with said thrust resisting means and having friction surfaces complemental to said element friction surfaces, respectively, said driving members connected to each other for simultaneous rotation and having their axial movement limited by said thrust resisting means in a direction tending to engage said complemental friction surfaces to said element friction surfaces, means including axially yieldable means providing a preload between said complemental and element friction surfaces, and means including said shaft for increasing said bias in proportion to the axial thrust on said shaft.

3. In combination, a shaft, means engaged with said shaft to selectively subject said shaft to each of opposite axial thrust loads, aV base, the shaft and the base being adapted for rotative movements relative to each other, torque limiting elements carried by and axially movable on said shaft and having friction faces, shaft driving elements engageable with and held axially by said base having friction surfaces adapted to engage said friction faces respectively, means axially biasing said torque limiting elements into engagement with said driving elements to establish a predetermined initial load on the associated friction surfaces and faces, and means including said shaft for increasing said bias in proportion to the axial thrust on said shaft.

4. In an actuator, the combination of a reversibly rotatable shaft including a threaded section and a mounting section, an annular member coaxial with said shaft and extending over a portion of said mounting section, said annular member having friction surfaces facing axially opposite each other, means for rotatably mounting said annular member to resist thrust in each axial direction, a driving gear operatively connected to said annular member, a pair of rings axially spaced from each other by said annular member around and secured to said shaft for rotation with and axial movement relative thereto, said rings having friction surfaces axially facing each other and adapted to engage the friction surfaces of said annular member, yieldable means for biasing said rings into engagement with said annular member for a predetermined load, and means including said shaft for increasing said bias in proportion to the axial thrust on said shaft.

5. In an actuator, the combination of an end structure having attaching means, driving means including an annular clutch member rotatably mounted in said structure and secured against axial movement relative thereto, a reversibly rotatable shaft including a longitudinal inner end section journaled in said annular clutch member and a screw section protruding from said clutch member, a movable element along said screw having means for attaching the other end of the actuator, a nut attached thereto and adapted t0 engage said screw for axial movement relative thereto, a pair of rings axially spaced from each other by said annular clutch member around and secured to said section for rotation therewith and axial movement relative thereto and having friction surfaces axially facing each other, one of said rings being backed by a shoulder on said section axially inward of said annular clutch member, adjustable yieldable means between the inner end of said section and the other of said rings to bias said ring friction surfaces into engagement with said annular clutch member for transmission of a predetermined torque, and means including said screw section for increasing the bias on said ring friction surfaces in response to axial load thrust. Y

LEONARD OCHTMAN.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,231,638 Nikonow July 3, 1917 1,517,285 Fishedick et al Dec. 2, 1924 2,259,437 Dean Oct. 21, 1941 2,379,878 Bronander July 10, 1945 2,391,470 May Dec. 25, 1945 2,407,537 Chapman Sept. 10, 1946 2,410,695 Warner Nov. 5, 1946 2,479,019 Ochtman Aug. 16, 1949 2,480,212 Baines Aug. 30, 1949 FOREIGN PATENTS Number Country Date 328,888 Germany Nov. 8, 1920 

